People throughout our society have become increasingly aware and concerned about the environmental issues that plague the world. The depletion of the ozone layer, the rain forests, and clean water are just a few of the environmental issues that are being addressed. One approach in addressing these issues includes preserving resources by recycling them. Consequently, the recycling industry has become instrumental to serving this need.
In the recycling field, one area of increasing interest is the reuse of wastepaper. Millions of tons of wastepaper are generated every year in the United States. Recycling this wastepaper can save countless trees, as well as provide other ecological and economic benefits. However, the key to reuse of this wastepaper is the removal of contaminants from the wastepaper, thereby facilitating the use of recycled or secondary fibers from the wastepaper.
The paper recycling industry encounters a variety of contaminants in wastepaper. Many of these contaminants adhere to paper fibers and therefore may cause problems during the recycling process. One such contaminant is “stickies”, which can come from synthetic and natural sources. Stickies typically are classified as hot melts, pressure-sensitive adhesives (PSAs), latexes, binders, pitch, and ink and combinations thereof. Stickies can also be classified as macrostickies or microstickies depending upon the size of the stickies.
Stickies may cause operational and product quality problems. Stickies can deposit on machine surfaces, such as wires, felts, press rolls, and drying cylinders, cause process upsets, hinder fiber bonding, and reduce product quality. Consequently, it is necessary to monitor and control stickies to improve papermaking operations and product quality.
The paper industry typically uses mechanical methods of dispersion, screening and cleaning for controlling stickies. Screens and centrifugal cleaners are typically used to remove or separate stickies and other debris from the process stream. Nevertheless, stickies still may be found in the process stream. These remaining stickies may be controlled through use of minerals such as talc or surface-active chemicals for modification, detackification, or pacification of the stickies. These minerals and chemicals contribute significantly to operating costs.
Macrostickies are stickies that are large enough to be screened out during the conventional screening process using, for example, a 0.0006″ screen. Macrostickies are most commonly monitored using a device know as a “Pulmac shive analyzer,” which screens out the macrostickies from the furnish and determines the macrostickies level through image analysis. This process usually takes several hours to complete, and is useful as an “after-the-fact” record of the macrostickies level. However, owing to the long analysis time required, this process cannot provide feedback during the pulping process such that actions can be initiated to respond to high stickies levels. Consequently, there are no reliable prior art methods for rapidly monitoring stickies levels in an incoming furnish.
Microstickies are small enough to traverse the screening and cleaning systems, and are principally responsible for operational and product quality problems. However, there does not appear to be any prior methods or devices for sensing microstickies.
Therefore, there is a need for a system and method for rapidly sensing microstickies. There is also a need for a system and method for monitoring microstickies levels such that the use of minerals and chemicals can be minimized during normal operations, and increased when an outbreak of microstickies occurs. There is yet another need for a system and method for sensing microstickies that can be performed easily and efficiently.